556
Bacterial Pathogenesis, Molecular Basis of
Tab. 1
Representative virulence factors/mechanisms and their functions.
Virulence
factor/mechanism
Organism(s)
Virulence function
Motility
Pseudomonas aeruginosa
Enhanced ability of motile organisms to
disseminate to other tissues.
Altered
lipopolysaccharide
side chains
Salmonella typhimurium
Inhibition of cell lysis by inhibiting the
formation of the activated
complement complex.
Proteases
Pseudomonas aeruginosa
Streptococcus pyogenes
Destruction of tissue for dissemination;
provision of nutrients.
Destruction of complement, antibodies,
and other host cell defense proteins.
Antigenic variation
Neisseria gonorrhoeae
Variation of surface proteins to evade
host antibody response.
Exotoxins
A–B types:
Corynebacterium
diphtheriae
Pseudomonas aeruginosa
Clostridium tetani
Vibrio cholerae
Membrane disrupting:
Listeria monocytogenes
Clostridium perfringens
Killing of host immune response cells
(phagocytes, PMNs, etc). Destruction
of tissue to enhance nutrient
availability and possible
dissemination to other sites.
Pili or Fmbriae
Pseudomonas aeruginosa
Escherichia coli
Vibrio cholerae
Adhesion to host cells and mucosal
tissue.
Nonpilus adhesins
Pseudomonas aeruginosa
Streptococcus pyogenes
Vibrio cholerae
Adhesion to cells and mucosal tissue.
Secreted
(siderophores) and
surface proteins that
bind iron
Escherichia coli
Pseudomonas aeruginosa
Yersinia pestis
Acquisition of iron from host sources.
Capsules
Streptococcus pneumoniae
Inhibit phagocytosis.
Decrease activation of complement.
Survival within
phagocytes
Salmonella typhimurium
Evasion of host immune response.
strategies and mechanisms to cause in-
fection and disease. While not applicable
in every case, almost all pathogens must
successfully complete a series of common
steps in order to flourish. First, a pathogen
must gain entry into the host. Second, the
pathogen must be able to establish itself
(colonize) and adhere to host cell tissues.
Third, the pathogen must be able to sur-
vive within the host. Fourth, the pathogen
must be able to cause cell or tissue damage.
Lastly, the pathogen must be able to dis-
seminate from the host in order to infect a
new host.
The process may appear to be simple,
but one must remember that pathogens
face considerable challenges in attempting
to complete the steps outlined above.
Almost immediately these organisms face
the task of outcompeting the normal
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